1. Field of the Invention
The invention is related to the field of universal joints and in particular to a telescopic triplan universal joint.
2. Description of the Prior Art
Telescopic triplan universal joints such as taught by Orain in U.S. Pat. Nos. 4,490,126; 4,619,628; and 4,828,534 have an outer joint member 10 and an inner joint member 12 as shown in FIGS. 1 and 2. The outer joint member 10 normally has three symmetrically disposed chambers, each chamber having a pair of opposing side walls. Each side wall in each chamber has a flat longitudinal guideway 14 which runs parallel to the axis of rotation of the outer joint member. The longitudinal guideways 14 are spatially separated and parallel to each other.
The inner joint member consists of a spider member 16 which may be connected to a shaft 18. The spider member 16 has three equally spaced radially extending trunnions 20. Each trunnion 20 extends into one of the chambers in the space between a pair of longitudinal guideways 14 as shown in FIG. 2.
Disposed between each trunnion 20 and the adjacent longitudinal guideway 14 is a button 22 and a planar roller bearing 24. As shown more clearly in FIG. 3, the button 22 has a concave surface which mates with the spherical surface of the trunnion 20 and a flat surface which engages the surface of the planar roller bearing 24 on the side opposite the longitudinal guideway 14. The planar roller bearing 24 has a rectangularly shaped cage 26 in which are journaled a plurality of needle bearings 28. The cage 26 also has a pair of lateral guides which are received in grooves provided on the opposite side of the longitudinal guideways 14 and a pair of transverse lips or stops 30 provided at its opposite ends to maintain the button 22 in contact with the surface of the planar roller bearing 24. The transverse stops 30 are to prevent the button 22 from being disengaged from the planar roller bearing 24 when the inner joint member 12 is displaced at an angle relative to the outer joint member 10. In the universal joint taught by Orain in U.S. Pat. No. 4,619,628 a spring (not shown) is used between the stops on the planar roller bearing and the button to help maintain the center of the planar roller bearing under the button.
The problem with these structures is that under high torque loads, the friction between the planar roller bearings and the longitudinal guideways 14 increases to the point where the lateral forces of the button acting on the stops 30 is sufficient to break the stops off causing a failure of the universal joint. The present invention is a solution to this problem.